The parts which have different shapes of the upper and lower surfaces, should be regularly lined up for processing on either one of the upper or lower surfaces thereof.
There have conventionally been proposed various kinds of devices which line up parts based on the shapes of the parts.
For example, Japanese Patent Laid Open No. 55-93722 discloses a device which evaluates the shapes of upper or rear sides of the parts, and turns over the parts if upper sides are non-desired ones.
However, since the upper and lower surfaces of the parts are evaluated by shapes thereof, the evaluations depend upon the shapes of the parts. Such a device is useful for the manufacturing of single parts, but could not be used for parts having the same or similar shapes on both surfaces